Imagine you have two sons. One year apart.
The older son is already in kindergarden. For him, going there alone was the first time ever he had to get out of his comfort zone and step into "the unknown". It's a character building moment.

Now one year later it's time for the younger son to go to kindergarden. Do you think it woud be a good move to send him to another place than your other son. Or alternatively not telling him anything about the older brother also being there beforehand.

Hypothesis:
Going to kindergarden / school alone for the first time in their life is a character building moment for children.
If a kid has the assurement that his older brother/sister is there too, then they dont have to step out of their comfort zone and miss this character building moment. Therefore their mental devolopment will not be as fast as the older sibling's.

So to not put one of them on a disadvantage and give them both the exact same chances you should make them both go through the same situations. (until a certein age ofc).

What do you misc. doctors and fathers of hypothetic (and real) children think?

Planning on breeding the most alpha sons.

Oldest son paved the way. My second son followed 2 years later. The only noticeable difference that I could attribute to your hypothesis is second son seems to have more anxiety when he has to do anything for the first time, or perform (like play his guitar on camera or in front of people). However he is very intelligent and athletic. My youngest son is 4 years younger and he literally doesn't give a phuck.

Just going from my own anecdotal experience having brothers that are a little over a year apart. They went to the same public schools and were even homeschooled together at one point. My youngest brother is still alpha AF srs. He joined the military and moved up the ranks, just rebuilt a van that looks like a tiny home on the inside by hand and just kind of does his own thing with no fuarks given. I think there are many other variables. Genetics plays a bigger role than we'd like to think as well I believe.

my first day of kindergarten i was crying like a bish and the teacher held my hand and my parents brought me there. it was a very warm sunny beautiful morning. I dont remember really ever leaving my house that early to go do something. this was on a military base in a foreign country. i remember standing in rows with other kids. the morning sun was breaking thru providing that golden hour type light. I remember there was a flag carrying as well. was a remarkable moment.

i also pissed my pants at this school multiple times

I honestly don't think it'll matter much. but since you're in germany, it's much more important to keep them out of chithole ghetto schools once they reach school age.

godspeed brah

True. Thinking of going no kids for this exact reason.
And for that DINK life (no homo).

Yeah that makes sense as anxiety ofen caused by a lack of experience. Looks like we're onto something.

Inb4 nobel price

OP, since you're in Germany, I think it's different there than it is here. Don't your kids go to Kindergarten all together from like 5-8 years old?

In the US kids go for one year, usually at 5 years old and then move to 1st grade the next year.

There's alot to be said about sibling order and how it dictates alot of the child's personality and choices. I took a psyc class that had alot about it, the prof was a local legend that had written alot about it.
Anyway, with that said, I think it's the natural order of things to let the 2nd or 3rd or whatever child naturally fit in, eg send him to the school where the first kid went.
Even if you don't, there's so much other stuff in life that he will experience as a younger brother that you won't be able to control.
Source: Dad of 2 young adult men, they couldn't be more different from each other.